fact sheet
Fluids in Sport
Why fluid is important
Water is essential for the human body. It is required to maintain
blood volume, regulate body temperature and allow muscle
contractions to take place. During exercise, the body maintains
its optimal body temperature through sweating. Heat is removed
from the body when beads of sweat on the skin evaporate, which
results in a loss of body fluid. Sweat production (and therefore
fluid loss) increases with a rise in ambient temperature and
humidity, as well as with an increase in exercise intensity. So
while sweat loss during exercise is essential for body temperature
regulation, it can lead to dehydration.
Drinking fluid during exercise is necessary to replace fluids lost
in sweat. However, in most (elite) cases the rates of sweat loss
are higher than the rate of fluid intake. This can lead to a fluid
deficit which ultimately increases the likelihood of dehydration.
Therefore, fluid guidelines should promote drinking more fluid
to reduce the deficit and potential performance detriments
associated with dehydration. However, it is also important to
acknowledge that it is possible to over-drink during exercise.
This highlights the importance of getting to know your sweat
rate and knowing how much you should be drinking. Your sports
dietitian can help to tailor an individual fluid plan for you.
Dehydration and Performance
As dehydration increases, there is a gradual reduction in physical
and mental performance. There is an in heart rate and body
temperature, and an increased perception of how hard the
exercise feels, especially when exercising in the heat. Impaired
skill level can also occur, along with mental fatigue. Studies show
that loss of fluid equal to 2% of body mass is sufficient to cause
a detectable decrease in performance (that’s a 1.4 kg loss in a 70
kg athlete). Dehydration of greater than 2% loss of body weight
increases the risk of nausea, vomiting, diarrhoea and other
gastro-intestinal problems during and after exercise.
Dehydration also reduces the rate of fluid absorption from the
intestines, making it more difficult to reverse the fluid deficit.
You may end up feeling bloated and sick if you delay fluid
replacement. It is impossible to ‘train’ or ‘toughen’ your body to
handle dehydration.
Can you drink too much?
Drinking more fluid than is comfortable (in any conditions) has
the potential to interfere with your performance. In cool weather
or when the exercise pace is gentle, the rate of sweat loss may
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be quite low. It is unnecessary and potentially dangerous to drink
at rates that are far greater than sweat losses. Over-hydration
during exercise is called hyponatraemia (dilute levels of sodium in
the bloodstream). Symptoms include headaches, disorientation,
coma, and in severe cases, death. It is important to note though
that this is relatively rare and dehydration is a much more
common issue for athletes.
Estimating your fluid losses
Knowing your sweat rate can give you an indication of how much
you should be drinking during exercise. Sports dietitians routinely
measure an athlete’s sweat rate during training and competition
in a range of environmental conditions, to provide them with the
information required to design an individual fluid plan.
A simple strategy to work out your individual fluid loss is as
follows:
• Weigh yourself in minimal clothing, as close to the start of
exercise as possible. Ideally you should empty your bladder
before weighing.
• Commence exercise session
• Weigh yourself at the end of your session, in minimal clothing
again, ensuring you towel off any excess sweat from your body,
pass urine and void your bowels if necessary.
• Your weight change during exercise reflects your total fluid loss;
i.e. the difference between your sweat losses and fluid intake.
Other minor losses come from breathing, spitting, vomiting and
other insignificant sources.
• Repeat this procedure under different training conditions to get
a good understanding of your individual fluid needs, for example
in hot vs. cold temperatures, high intensity vs. low intensity
sessions.
• Remember that weight loss during exercise is primarily water
loss (not fat loss), and needs to be replaced soon after finishing
exercise.
How Much Fluid and When?
Drinking fluid during exercise helps to prevent a drop in
performance caused by dehydration, and fluid after exercise
will re-hydrate you. The amount of fluid and the timing of drinks
depend on the individual and the sport.
Here are some tips:
• Always start exercise well hydrated; this will lower the risk
of becoming dehydrated during sport. Urine colour can be
indicative of hydration status.
fact sheet
Fluids in Sport
• Aim for a pale yellow colour, as dark urine can represent a
dehydrated state. There is minimal performance benefit to
being over-hydrated as drinking excessive amounts of fluid
before exercise causes increased urination and feeling bloated.
• Develop a plan for drinking during exercise based on your own
fluid losses and sweat rates.
• Immediately after exercise, monitor your weight change to
estimate your final fluid deficit. During recovery, you will
continue to lose fluids through sweating and urine losses,
so plan to replace 125-150% of this fluid deficit over the next
2-6 hours. For example, if you lost 1 kg (1000mL), you will
need to drink 1250-1500mL to fully re-hydrate. Drink fluids in
conjunction with your recovery snacks and meal to achieve this
goal.
• Different sports pose different challenges and opportunities for
optimal hydration. For team and racquet sports there are formal
breaks between play, with substitutions and time-outs, all
offering an opportunity to drink. Some individual sports require
you to drink on the move. Be smart and practice strategies to
get maximum benefit from fluid intake with minimal fuss and
discomfort. Try special squeeze bottles, or hands free drink
pouches if practical.
• Thirst is not an effective indicator of hydration status while
exercising. There is usually a significant fluid loss before you
feel thirsty. When drinking, your thirst will be satisfied well
before these losses have been fully replaced. Therefore, it is
important to practice a fluid intake plan that is appropriate for
you.
sporting situations.
Of course, salt can be consumed in foods that are eaten at the
same time as post-exercise fluids.
For more information, see the SDA fact sheet on Sports Drinks.
What is the best fluid to drink?
The detrimental effects of dehydration on performance may
include:
• Loss of coordination, impaired ability to make a decision,
increased rate of perceived exertion and increased risk of heat
stress.
• Aim to match your sweat rate and fluid loss with fluid intake as
closely as possible.
• Get to know your fluid loss by weighing yourself before and after
training sessions and competition.
• Ensure that you drink at a rate that is comfortable.
• Practice your competition fluid intake plan in training sessions.
• Water is an excellent fluid for low intensity and short duration
sports.
• Sports drinks are ideally suited to high intensity and endurance
sports.
• Drink alcohol sensibly and assess the detrimental effects on
your recovery.
As there are many drink options available, you now need to think
about which is best for you. Plain water alone is an effective
drink for fluid replacement, especially in low intensity and short
duration sports. However, if carbohydrate and electrolytes
are added to water, as in a sports drink, performance can be
enhanced, especially in high intensity and endurance sports.
Carbohydrate provides an important energy source for muscles
and the brain, as well as enhancing flavour. This can be one
advantage of a sports drink over plain water; a flavoured drink
is generally consumed in greater quantity than a non-flavoured
drink.
Electrolytes such as sodium are lost in sweat and need to be
replaced during and after prolonged exercise. Sodium in fluid
improves fluid intake as it stimulates the thirst mechanism,
promotes both carbohydrate and water uptake in the intestines,
and reduces the volume of urine produced post-exercise. Sports
drinks contain appropriate amounts of electrolytes for most
Caffeine
There are a growing number of drinks on the market that contain
a number of ingredients including caffeine. Caffeine is no longer
banned by the World Anti Doping Agency. The consumption of
small to moderate doses of caffeine (75 - 200 mg) can help to
sustain exercise performance, reduce the perception of effort,
and is unlikely to alter hydration status during exercise in such
doses. However, the use of caffeine amongst athletes is often ad
hoc and they may be unaware of the potential detrimental side
effects associated with its use. Ensure that you discuss the use of
caffeine with your sports dietitian or sports scientist and consider
individual responses to caffeine.
Alcohol
Alcohol is not a suitable fluid to choose immediately after
exercise, as it impairs vital recovery processes, and may also
impair the ability to rehydrate effectively post-exercise. If you
choose to drink alcohol after exercise, look after your recovery
needs first (i.e. replacing fluids, carbohydrate stores and
consuming some protein to assist with muscle repair) and then
consume alcohol in sensible amounts. However, if a soft-tissue
injury is suspected, alcohol should be avoided as it can increase
swelling and counter recovery goals.
Fluid Guidelines Summary
May 2011
© This is a sports nutrition publication of Sports
Dietitians Australia.
www.sportsdietitians.com.au